1. Technical Background
The present invention relates generally to medical devices, and more particularly to a stent delivery catheter system.
2. Discussion
Catheter systems are used in a variety of therapeutic applications, including many vascular treatments. Various types of catheters are available, such as balloon catheters for procedures such as angioplasty. Angioplasty can be used to treat vascular disease, in which blood vessels are partially or totally or partially blocked or narrowed by a lesion or stenosis. By way of example, the present invention will be described in relation to coronary and peripheral angioplasty and other vascular treatments. The coronary procedure is often referred to as PTCA, which stands for "percutaneous transluminal coronary angioplasty". However, it should be understood that the present invention relates to any stent delivery system having the features of the present invention, and is not limited to angioplasty.
Most balloon catheters have a relatively long and flexible tubular shaft defining one or more passages or lumens, and an inflatable balloon attached near one end of the shaft. This end of the catheter where the balloon is located is customarily referred to as the "distal" end, while the other end is called the "proximal" end. The balloon is connected to one of the lumens extending through the shaft for the purpose of selectively inflating and deflating the balloon. The other end of this inflation lumen leads to a hub coupling at the other end for connecting the shaft lumens to various equipment. Examples of this type of balloon catheter are shown in U.S. Pat. No. 5,304,197, entitled "Balloons For Medical Devices And Fabrication Thereof," issued to Pinchuk et al. on Apr. 19, 1994; and also in U.S. Pat. No. 5,370,615, entitled "Balloon Catheter For Angioplasty," issued to Johnson on Dec. 6, 1994.
A common treatment method for using such a balloon catheter is to advance the catheter into the body of a patient, by directing the catheter distal end percutaneously through an incision and along a body passage until the balloon is located within the desired site. The term "desired site" refers to the location in the patient's body currently selected for treatment by a health care professional. After the balloon is disposed within the desired site, it can be selectively inflated to press outward on the body passage at a relatively high pressure to a relatively constant diameter, in the case of an inelastic or non-compliant balloon material.
This outward pressing of a constriction or narrowing at the desired site in a body passage is intended to partially or completely re-open or dilate that body passageway or lumen, increasing its inner diameter or cross-sectional area. The narrowing of the body passageway lumen is called a lesion or stenosis, and may be formed of hard plaque or viscous thrombus. In the case of a blood vessel, this procedure is referred to as angioplasty. The objective of this procedure is to increase the inner diameter or cross-sectional area of the vessel passage or lumen through which blood flows, to encourage greater blood flow through the newly expanded vessel.
In some cases, a flexible cylinder or scaffold made of metal or polymers, which is called a stent, may be permanently implanted into the vessel following an angioplasty procedure. The stent tends to hold the lumen open longer, to reinforce the vessel wall and improve blood flow.
To improve efficiency and reduce time required for the vascular procedure, it is desirable to combine these two procedures, angioplasty and stent deployment. This combined procedure may be referred to as "primary stenting" or "direct stenting." Several benefits may be realized by employing such a combined procedure, including reduced time of the procedure, less intervention, and fewer medical devices inserted into the patient's body.
During a primary stenting procedure, an initial angioplasty is not performed. Rather, a modified stent delivery system is used to cross or traverse a lesion or stenosis, expand the desired site in a fashion similar to angioplasty and deploy a stent, all in a single, unified procedure. In this direct stenting procedure, the stent delivery system is first advanced within the patient's body until the stent is located within the desired site, where the lesion or stenosis is present.
Of course, the operating environment for the stent delivery system may be more difficult when the initial broadening angioplasty or "pre-dilatation" is absent. In other words, the vessel may be narrowed or blocked, and the lesion or stenosis may even be calcified or hardened. The stent delivery system should preferably have a mechanism for more successfully traversing a more difficult environment. After crossing the lesion, the stent delivery system balloon is inflated to expand the stent, followed by deflation of the balloon and withdrawal of the stent delivery system.
Previously known stent delivery systems may have been merely a balloon catheter having a stent mounted and crimped onto the deflated balloon. Such elegantly simple devices have been sufficient for many applications, but a more sophisticated system may be desirable in more challenging cases and environments.
Friction forces may tend to cause a crimped stent to slip in a proximal direction while the catheter system is advanced, or to slip in a distal direction if the physician decides to withdraw the stent without deploying it. It is of course desirable to retain the stent securely in the proper position.
The stent delivery system should also preferably protect the stent from damage or deformation during this period. It is further desirable that the stent delivery system should be able to push through and traverse as many different anatomical arrangements and stenosis configurations as possible. Moreover, the stent delivery system should preferably have a positive mechanism for holding and then releasing, expanding, and deploying the stent at the desired site.
Accordingly, the stent delivery system also desirably includes a mechanism for securing the stent in the form of a sheath, capable of completely covering the crimped stent during insertion. This sheath is permanently mounted about the balloon catheter, yet able to slide in a proximal direction from the stent-covering position, to uncover the stent during inflation of the balloon and expansion of the stent.
Prior stent delivery systems were often designed for the smallest possible outer diameter or profile at the distal end. The small profile was preferred for access into small vessels following angioplasty. In addition, prior stent delivery systems generally provided distal tips which were as short as possible, sometime extending only a few millimeters beyond the distal balloon leg.
However, the present direct stent delivery system preferably contradicts these prior design ideas by providing an enlarged and lengthened, flexible tapering tip. This distal tip tapers gradually up to an outer diameter preferably equal to the largest outer diameter of the entire system, and tends to gently widen any particularly narrow stenoses.
In addition, the sheath should have sufficient wall thickness to push distally against a portion of the flexible tip, to increase the column strength of the stent delivery system. This enhanced "pushability" better enables the stent delivery system to traverse and cross a lesion or stenosis.
In addition, the stent delivery system should provide for high visibility under fluoroscopy. Often the stent delivery system will be used in conjunction with an outer guiding catheter, which surrounds and guides the stent delivery system into a position near the desired site. The visibility of the stent delivery system may be affected by the size of the lumen through which radiopaque contrast fluid is injected. This fluid shows up on a fluoroscope, and is generally injected through the annular space between the inner wall of the guiding catheter and the outer surface of the stent delivery system. The visibility of the stent delivery system under fluoroscopy can therefore preferably be increased by reducing the outer diameter of the stent delivery system along a major portion of all of its length.
Accordingly, the present invention preferably provides a direct stent delivery system for delivering and deploying a stent. This stent delivery system preferably also provides enhanced stent position retention, as well as stent protection, during longitudinal movement of the catheter.
The stent delivery system also is preferably capable of traversing total vessel occlusions, preferably having enhanced pushability and a positive stent release mechanism.
The stent delivery system also preferably has a high visibility arrangement for the injection of radiopaque contrast medium.
These and various other objects, advantages and features of the invention will become apparent from the following description and claims, when considered in conjunction with the appended drawings.